that in a report in the journal "science." we asked ben tracey and our los angeles bureau to tell us what that will mean to the rise of the seas. >> reporter: the researchers, including nasa scientists, say antarctica and greenland have lost nearly five trillion tons of ice since 1992, causing sea levels to rise by nearly half an inch. >> we didn't really know that we were going to find such a dramatic speed-up. >> reporter: nasa's erik ivins worked on the study. scientists say human activity, such as burning fossil fuels, is warming the atmosphere. >> each year, we're getting longer and longer melt seasons. this year, we had one of the longest melt seasons that we've ever seen. >> reporter: melting ice sheets now account for 30% of the rise in ocean levels, making flooding from storms such as hurricane sandy even more destructive. along the california coast, the ocean is expected to rise another three to five feet by the end of the century. 3.5 million confidential californians live within three feet of sea level. >> eventual